Anti-Dive

AssBurns

will wheel for beer
Staff member
Joined
Oct 1, 2018
Messages
7,959
Age
31
Location
Yucaipa, CA
I'm working on building my own long travel suspension, and while I'm at it I'd like to dial in the geometry a little better while I have the chance. So my question is about Anti-Dive. I notice that pretty much all of the "Go-Fast" vehicles have 0% Anti-Dive. Even most of the Ultra4 IFS buggies have 0% Anti-Dive it looks like. Looking at Jorgan Pellegrino's IFS/IRS U4 car has negative Anti-Dive %(Pro-Dive?). Then I look at the solid axle/rock crawler guys and some of them are running 50%-200% anti-dive. I know solid axle is a whom other animal but I figured I'd throw that out there for comparison sake. Sounds like having parallel arms is the way to go. It helps avoid bump steer since the caster doesn't change throughout the suspension cycle and you don't have to worry about caster curve. I'm just wondering how it will handle on the street compared to having some anti-dive built in? I don't plan on a lot of street driving but I do plan on driving on the street to get to trails sometimes. It'll mostly be on a trailer these days though. I hear you can mitigate the "Dive" by tuning your spring rates and bypasses to help reduce the dive in the front end. I just don't know exactly what is needed to be done. Just higher spring rates and stiffer low speed valving?

Something to point out as well. There are two separate forces that effect front end dive. Both can be tuned by the suspension geometry and are related to each other. The first one is the one you can see by playing with the basic suspension calculators. (Triaged 3 and 4 link calculators will show this form of anti-dive/anti-squat). This anti-dive is the exact opposite of anti-squat. The forces are just applied in the opposite direction since it's on the front end of the vehicle and happens during deceleration. This is effected by the suspension geometry and its relation to the COG (Center of Gravity). This is inertia induced anti-dive.
The second one seems to be a more important one based on my readings, but it's harder to calculate without expensive software. It can be brought to a neutral position easily by having 0% anti-dive (parallel links/arms from side view and level with the ground.) On IFS cars, this anti-dive or lack thereof can be constant throughout suspension cycle since the arms stay parallel and level with the ground (when viewed from the side). On solid axle vehicles this number will change throughout suspension cycle since the arms change angle as the suspension cycles. The way this Anti-Dive works is when you apply the brakes, the spindle will want to rotate forward. If there is anti-dive (picture upper arm slanted back, sloping down towards the back). As the spindle wants to rotate as the brake force is applied, the rotation of the spindle will want to pull the upper arm down and forward. This causes the suspension to want to push down/lift the chassis up. This force is known as anti-dive. It is torque induced instead of inertia induced liked I mentioned above. This seems to have a greater effect on suspension than the inertia induced anti-dive. Having the links or arms parallel and level with the ground gives a 0% Anti-Dive in both forms.

Here is a link to a good thread on this stuff. Where I got a lot of my information on this. - http://www.4x4-16.com/Basic-IFS-IRS-anti-squat-dive-tech-with-a-twist_10823326-2.html

There are some really good illistrations in that thread too. I will pull some over here when I get some more time.
 

Arcticelf

Head BFH Operator at Gray Man Fab
Joined
Apr 23, 2019
Messages
1,167
Location
DelCo PA
Check out "high speed vehicle dynamics" it's got a very good description of calculating these factors, and why the trade offs they create.

If you're running no anti-dive you need stronger springs to avoid excessive nose-dive under breaking (this is an issue on or off road), which makes the ride harsher. But you're right about the benefits of no anti-dive for the rest of the geometry. It also makes the design simpler.
 

AssBurns

will wheel for beer
Staff member
Joined
Oct 1, 2018
Messages
7,959
Age
31
Location
Yucaipa, CA
Check out "high speed vehicle dynamics" it's got a very good description of calculating these factors, and why the trade offs they create.

If you're running no anti-dive you need stronger springs to avoid excessive nose-dive under breaking (this is an issue on or off road), which makes the ride harsher. But you're right about the benefits of no anti-dive for the rest of the geometry. It also makes the design simpler.
Thanks I’ll check that out tomorrow when I get some time.

I figured stiffer springs would be needed due to the nature of no anti-dive. Same thing for bypasses too I’m assuming. I’ve heard multiple people say that you need bypasses if you run no anti-dive but I feel it mostly requires a higher spring rate, not necessarily bypasses. Maybe just firmer valving. I’ll be building my suspension for bypasses but I want to learn more about why people say they are needed without anti-dive
 

Arcticelf

Head BFH Operator at Gray Man Fab
Joined
Apr 23, 2019
Messages
1,167
Location
DelCo PA
Thanks I’ll check that out tomorrow when I get some time.

I figured stiffer springs would be needed due to the nature of no anti-dive. Same thing for bypasses too I’m assuming. I’ve heard multiple people say that you need bypasses if you run no anti-dive but I feel it mostly requires a higher spring rate, not necessarily bypasses. Maybe just firmer valving. I’ll be building my suspension for bypasses but I want to learn more about why people say they are needed without anti-dive

Also check out "Race Car Vehicle Dynamics" published by the SAE, it's a graduate level textbook, took me about a month and a bottle of good scotch to work through.

Bypass shocks would let you have a beat of both worlds setup: in the middle zone you'll have more body movement for a nicer ride (like a car with anti-dive) and when you get on the brakes the stiffer compression zones will kick in to simulate anti-dive.

That's probably part of the reasons TTs can run with no anti-dive on an IFS, and not have unacceptable nose dive.
 

AssBurns

will wheel for beer
Staff member
Joined
Oct 1, 2018
Messages
7,959
Age
31
Location
Yucaipa, CA
Also check out "Race Car Vehicle Dynamics" published by the SAE, it's a graduate level textbook, took me about a month and a bottle of good scotch to work through.

Bypass shocks would let you have a beat of both worlds setup: in the middle zone you'll have more body movement for a nicer ride (like a car with anti-dive) and when you get on the brakes the stiffer compression zones will kick in to simulate anti-dive.

That's probably part of the reasons TTs can run with no anti-dive on an IFS, and not have unacceptable nose dive.
Gotcha, that totally makes sense. Thanks.

I’ve been meaning to pick up one of those suspension/chassis design books but haven’t yet. They are so damn expensive for a book. And the Carroll Smith book is like 2-3x more expensive! Sure it’s a good resource but damn that’s hard to justify spending hundreds of dollars on a book when I can buy some software to help plug in my numbers.
 

Arcticelf

Head BFH Operator at Gray Man Fab
Joined
Apr 23, 2019
Messages
1,167
Location
DelCo PA
Gotcha, that totally makes sense. Thanks.

I’ve been meaning to pick up one of those suspension/chassis design books but haven’t yet. They are so damn expensive for a book. And the Carroll Smith book is like 2-3x more expensive! Sure it’s a good resource but damn that’s hard to justify spending hundreds of dollars on a book when I can buy some software to help plug in my numbers.

The books are expensive, that SAE one is the best, I bought a bunch of them this winter. I'll loan it to you if you want, I'm not really using it right now. Shoot me a PM and I'll drop it in the mail, just send it back when you're done.

The book learnin' to understand why, the software is to do your design.
 

madtaco461

BRO-runner
Joined
Oct 6, 2018
Messages
3,803
Age
39
Location
Socal
That SAE book looks amazing. Just read through the index. Looks like you can find a hardcover used under $100. I have the pdf carroll smith tune to win.

Here his Anti Dive /Anti Squat read.

ASAD1.pngASAD2.pngASAD3.png
 

Arcticelf

Head BFH Operator at Gray Man Fab
Joined
Apr 23, 2019
Messages
1,167
Location
DelCo PA
I need to read that book.

Also, I think Mr. Shelby effectively answers the question of why we want no anti-dive. All the issues he's discussing for a track car will be much, much worse on the dirt.
 

AssBurns

will wheel for beer
Staff member
Joined
Oct 1, 2018
Messages
7,959
Age
31
Location
Yucaipa, CA
http://users.telenet.be/AudiR8/Carroll Smith - Tune to win OCR.pdf
The link is still live. Go download it.

edit nevermind. PM me your email

second edit... this one works
Sweet. Thanks dude! I got some reading to do. I'd like to create a couple threads like this to discuss different parts of suspension geometry. For me to learn, but also for others to be able to learn from as well. As I'm reading the book, I'll probably just end up having more/better questions and I'll post em up here.
 
Top Bottom